798 CDX-585, A bispecific antibody with dual targeting of ILT4 and PD-1 checkpoint pathways

Background

Activation of the ITIM-bearing ILT4/LILRB2 receptor by its cognate ligands (HLA-G and HLA Class I) has been postulated as a resistance mechanism for checkpoint blockade of PD-1 and CTLA-4. Dual inhibition of receptors that suppress myeloid and T cell compartments through the generation of bispecific antibodies (bsAbs) is a promising strategy to improve outcomes for patients whose tumors are resistant to checkpoint inhibition.

Methods

We describe the discovery and characterization of CDX-585 a bsAb developed from novel ILT4 and PD-1 antagonist mAbs that revert myeloid cell suppression by antagonizing ILT4 and activating T-cell responses through PD-1 inhibition. The bsAb was engineered as a tetravalent molecule using the PD-1 IgG1 mAb linked to scFv of the ILT4 mAb at the C-terminus of the heavy chain. A series of mutations were introduced in the Fc domain to eliminate Fcy receptor binding and increase affinity to the neonatal Fc receptor. CDX-585 has good biophysical characteristics and retains functional properties similar to, or better, than the parental mAbs.

Results

CDX-585 has sub-nanomolar affinity binding to ILT4 and PD-1 and is a potent competitor of their respective ligands. Primary cultures of human macrophages and dendritic cells treated with CDX-585 enhanced production of inflammatory cytokines/chemokines, which was further potentiated in the presence of toll like receptor activation with lipopolysaccharide (LPS). CDX-585 was particularly effective in promoting T cell activation as measured by mixed lymphocyte reactions, and in polarizing macrophages towards M1 based on their cytokine profile. Pilot studies in mice and cynomolgus macaques confirmed a favorable pharmacokinetic profile without adverse effects of treatment noted in clinical observations or clinical chemistry.

Conclusions

CDX-585 effectively combines ILT4 and PD-1 blockade into one molecule with favorable biophysical and functional characteristics supporting the initiation of development activities including manufacturing and IND-enabling studies.

Abstract 1865: Simultaneous de-repression of innate and adaptive immune responses through dual targeting of ILT4 and PD(L)-1 with bispecific antibodies

Activation of innate immunity using targeted therapies has become an attractive approach to stimulate antitumor responses. Dual inhibition of receptors that suppress myeloid and T cell compartments through the generation of bispecific antibodies (bsAbs) is a promising strategy to overcome resistance to checkpoint inhibition. Activation of the ITIM-bearing ILT4/LILRB2 receptor by its cognate ligands (HLA-G and HLA Class I) in myeloid cells induces a strong immunosuppressive response that may be leveraged by tumors to evade immune surveillance. Monoclonal antibodies (mAbs) that inhibit ILT4 activity have demonstrated promising preclinical and early clinical data in combination with PD-1 inhibitors, including in the checkpoint refractory setting. These findings provide a rationale to co-target ILT4 with PD(L)-1 using a single molecule. We describe the discovery and characterization of ILT4 inhibitory mAbs for engineering bsAbs that revert myeloid cell suppression by antagonizing ILT4 and activate T cell responses through PD(L)-1 inhibition. Humanized anti-ILT4 mAbs were generated that specifically bind human and macaque ILT4. These mAbs exhibit sub-nanomolar HLA-G binding to ILT4 expressing cells. Macrophages treated with ILT4 mAbs release inflammatory cytokines/chemokines and upregulate activation markers resulting in polarization to an M1 inflammatory phenotype. These activities are further potentiated in the presence of toll-like receptor activation with lipopolysaccharide (LPS). We engineered tetravalent bsAbs using an Fc-silenced IgG1 linked to scFv format from our anti-ILT4 and anti-PD-L1 mAbs in both orientations. The bsAbs have good biophysical characteristics and retain functional properties similar to the parental mAbs. Further in vitro and in vivo characterization efforts are ongoing to select the bsAb candidate to enter development activities and IND-enabling studies.

Citation Format: Laura Vitale, Mike Murphy, Jeff Weidlick, Anna Wasiuk, Thomas O'Neill, Jenifer Widger, Laura Mills-Chen, Andrea Crocker, Colleen Patterson, James Boyer, Linda Crew, Edward J. Natoli, Jay S. Lillquist, Joel Goldstein, Lawrence J. Thomas, Henry C. Marsh, Diego Alvarado, Tibor Keler. Simultaneous de-repression of innate and adaptive immune responses through dual targeting of ILT4 and PD(L)-1 with bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1865.

Conditioning treatment with CD27 Ab enhances expansion and antitumor activity of adoptively transferred T cells in mice

Cyclophosphamide plus fludarabine (C/F) are currently used to improve the expansion and effectiveness of adoptive cell therapy (ACT). However, these chemotherapeutics cause pan-leukopenia and adverse events, suggesting that safer and more effective conditioning treatments are needed to improve ACT outcomes. Previously, we reported that varlilumab, a CD27-targeting antibody, mediates T_reg -preferential T cell depletion, CD8-T cell dominant costimulation, and systemic immune activation in hCD27 transgenic mice and cancer patients. We reasoned that the activities induced by varlilumab may provide an effective conditioning regimen for ACT. Varlilumab pretreatment of hCD27^+/+mCD27 ^{− /−} mice resulted in prominent proliferation of transferred T cells isolated from wild-type mice. These studies uncovered a critical role for CD27 signaling for the expansion of transferred T cells, as transfer of T cells from CD27 deficient mice or treatment with a CD70 blocking antibody greatly reduced their proliferation. In this model, varlilumab depletes endogenous hCD27^+/+ T cells and blocks their subsequent access to CD70, allowing for more CD70 costimulation available to the mCD27^+/+ transferred T cells. CD27-targeted depletion led to a greater expansion of transferred T cells compared to C/F conditioning and resulted in longer median survival and more cures than C/F conditioning in the E.G7 tumor model receiving OT-I cell therapy. We propose that translation of this work could be achieved through engineering of T cells for ACT to abrogate varlilumab binding but preserve CD70 ligation. Thus, varlilumab could be an option to chemotherapy as a conditioning regimen for ACT.

Development of CDX-527: a bispecific antibody combining PD-1 blockade and CD27 costimulation for cancer immunotherapy

CD27 is a costimulatory molecule that provides a complementary target to the PD-1/PD-L1 checkpoint axis on T cells. Combining a CD27 agonist antibody with PD-1/PD-L1 blockade has shown synergistic antitumor activity in preclinical models, which led to clinical studies of the combination in cancer patients. We theorized that coupling CD27 costimulation with PD-1/PD-L1 blockade in a bispecific antibody (BsAb) may provide greater immune activating properties than combining the individual mAbs due to enhanced CD27 activation by cross-linking through PD-L1 and Fc receptors. To test this approach, we developed CDX-527, a tetravalent PD-L1xCD27 IgG1-scFv BsAb. CDX-527 potently inhibits PD-1 signaling and induces CD27-mediated T cell costimulation through PD-L1 cross-linking. In mixed lymphocyte reaction assays, CDX-527 is more potent than the combination of the parental antibodies, suggesting that cross-linking through both Fc receptors and PD-L1 results in enhanced CD27 agonist activity. CDX-527 was shown to mediate effector function against tumor cells overexpressing either CD27 or PD-L1. In human CD27 transgenic mice, we observed that antigen-specific T cell responses to a vaccine are greatly enhanced with a surrogate PD-L1xCD27 BsAb. Furthermore, the BsAb exhibits greater antitumor activity than the combination of the parental antibodies in a syngeneic lymphoma model. A pilot study of CDX-527 in cynomolgus macaques confirmed a mAb-like pharmacokinetic profile without noted toxicities. These studies demonstrate that CDX-527 effectively combines PD-1 blockade and CD27 costimulation into one molecule that is more potent than combination of the parental antibodies providing the rationale to advance this BsAb toward clinical studies in cancer patients.

Abstract 1555: Monoclonal antibodies targeting the TAM family of receptor tyrosine kinases

The TAM receptors (Tyro3/Axl/MerTK) family of receptor tyrosine kinases (RTKs) are important negative regulators of innate immunity. TAM receptor activation in myeloid cells by its ligands Gas6 or Protein S (PROS) promotes phosphatidylserine-dependent efferocytosis of apoptotic cells, inducing a tolerogenic state and mediating resolution of inflammation. TAM-deficient mice exhibit phenotypes consistent with systemic inflammation and autoimmunity. Importantly, individual ablation of TAM receptors can confer tumor immunity, increased pro-inflammatory cytokines and tumor lymphocyte infiltration, leading to the proposal that TAM receptors act as checkpoints of innate immunity. We hypothesize that pharmacological targeting of this family of receptors with monoclonal antibodies (mAbs) may lead to a similar pro-inflammatory response and recapitulate the antitumor effects observed in TAM-deficient mice. From a panel of human anti-MerTK, Axl or Tyro3 mAbs derived from phage-display libraries or human IgG expressing mice we identified unique mAbs that markedly enhanced cytokine and chemokine release from primary human immune cells, alone or in the presence of inflammatory stimuli. Interestingly, the qualitative and quantitative pattern of cytokine response from dendritic cells was very similar using antibodies targeting the individual TAM receptors, and also similar to activation of dendritic cells using a CD40 agonist mAb, suggesting that TAM-targeting mAbs can promote immune activation. We identified surrogate mAbs targeting mouse TAM receptors that elicited similar responses in vivo, and demonstrated antitumor activity when dosed alone, or in combination with PD-1/L1 blockade in syngeneic tumor models. In addition, human MerTK transgenic, and TAM knockout mice have been generated and characterized in order to establish in vivo proof-of-concept with human TAM mAbs. Overall, pharmacological modulation of TAM receptors with mAbs enhances cytokine production in human and murine model systems consistent with the published role of TAMs as negative regulators of innate immunity. Mechanistic and proof-of-concept studies support further development of these mAbs as novel approaches to overcome these checkpoints of the innate immune response.

Citation Format: Diego Alvarado, Laura Vitale, Mike Murphy, Thomas O'Neill, Andrew Proffitt, Jay Lillquist, Gwenda Ligon, Komal Patel, Anna Wasiuk, Jeff Weidlick, Jenifer Widger, Laura Mills-Chen, Andrea Crocker, Colleen Patterson, Russell A. Hammond, Li-Zhen He, Joel Goldstein, Lawrence J. Thomas, Henry C. Marsh, Tibor Keler, Richard Gedrich. Monoclonal antibodies targeting the TAM family of receptor tyrosine kinases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1555.

Abstract 3217: Preclinical evaluation of the recombinant dendritic cell growth factor CDX-301 (Flt3L), and AST-008, a TLR9 agonist SNA

Recent studies have highlighted the critical role of CD103+/CD141+ dendritic cells (DCs) in antitumor immunity. CDX-301 is a soluble, recombinant human FLT3 ligand (Flt3L). Flt3L is a hematopoietic cytokine which stimulates the proliferation and differentiation of various blood cell progenitors, including CD103+/CD141+ DCs. CDX-301 is in clinical development for multiple cancers and may hold significant opportunity for synergistic development in combination with other immunotherapies, in particular toll-like receptor 9 (TLR9) agonists that are known to promote maturation and activation of DCs. AST-008 is a TLR9 agonist oligonucleotide in a spherical nucleic acid (SNA) format and is in clinical development for multiple cancers in combination with pembrolizumab. SNAs are densely packed, radial arrangements of oligonucleotides around a nanoparticle core. SNAs have increased cellular uptake, nuclease stability, and affinity to targets compared with linear oligonucleotides. AST-008 induces potent TH1-type immune responses in vitro, in mice and non-human primates, and has shown potent antitumor activity as a monotherapy and enhanced checkpoint inhibitor activity in several murine tumor models. AST-008 increases tumor-infiltrating lymphocytes, interferon-inducible gene expression, and activation and expansion of CD8+ T cells with reduced T-regulatory cells in the tumor microenvironment. We examined the effects of the combination of CDX-301 and a murine version of AST-008, muAST-008, in mice on DCs and on antitumor efficacy in a tumor model. Mice were implanted with MC38 murine colon adenocarcinoma tumor cells (day 0) and animals were treated with either CDX-301 (5 μg, days 2-8 i.p.) only, muAST-008 only (1 mg/kg or 3 mg/kg, days 9, 16, 23 and 30 p.t.), or the combination of CDX-301 (5 μg, days 2-8) with muAST-008 (1 mg/kg or 3 mg/kg, days 9, 16, 23 and 30). Treatment with CDX-301 and muAST-008 showed an additive effect in retarding tumor growth and prolonging survival. To help understand the mechanisms involved in the antitumor effects, animals were treated with a similar course of CDX-301 and muAST-008 and spleens were harvested for flow cytometry evaluation 2 days after the last CDX-301 dose. For these studies, we also included a second DC activating agent, an agonist anti-CD40 mAb FGK45.5 (50 μg i.p. together with the last dose of CDX-301) among the combinations. We observed a significant increase in the percentage of CD103+CD8+ cDCs by the addition of muAST-008 to CDX-301 treatment. In addition, muAST-008 led to the up-regulation of activation markers on dendritic cells, which was markedly enhanced when combined with CD40 activation. These data demonstrate that muAST-008 leads to systemic activation of CDX-301 expanded DCs, leading to more potent anti-tumor immunity and support the potential of combining CDX-301 and AST-008 in augmenting the immunotherapy of cancers.

Citation Format: Lawrence J. Thomas, Li-Zhen He, Lauren E. Gergel, Eric M. Forsberg, Elizabeth Q. Do, James M. Boyer, April R. Baronas, Mallary Rocheleau, Kathleen M. Borrelli, Anna Wasiuk, Jeffrey Weidlick, Henry C. Marsh, Bart R. Anderson, SubbaRao Nallagatla, Richard Kang, Ekambar R. Kandimalla, Tibor Keler. Preclinical evaluation of the recombinant dendritic cell growth factor CDX-301 (Flt3L), and AST-008, a TLR9 agonist SNA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3217.

Abstract 2392: CDX-527: A novel bispecific immune-modulating antibody targeting CD27 and PD-L1

CD27 is a costimulatory molecule that provides a complementary target to the PD-1/PD-L1 axis on T cells. Combining a CD27 agonist monoclonal antibody (mAb) with PD-1/PD-L1 blockade has been shown to promote synergistic antitumor activity in preclinical models. In advanced cancer patients, the combination of the CD27 agonist mAb, varlilumab, with the PD-1 mAb, nivolumab, was generally well tolerated, induced strong biological effects, and led to sustained clinical responses in some patients that generally have low response rates to checkpoint inhibitors. We theorized that combining CD27 costimulation with PD-1/PD-L1 blockade in a bispecific antibody (bsAb) may provide greater immune activating properties than combining the individual mAbs due to enhanced CD27 activation by crosslinking through PD-L1 in addition to Fc receptors. To test this approach, we developed CDX-527, a tetravalent human anti-CD27/PD-L1 IgG1 bsAb. CDX-527 inhibits PD-1 signaling in vitro in a manner similar to clinically approved PD-1/PD-L1 antibodies. CDX-527 also elicits potent T cell costimulation through PD-L1 crosslinking as measured by cytokine induction and cell proliferation, whereas the PD-L1 or CD27 parental antibodies show no significant activity. In a mixed lymphocyte reaction assay, CDX-527 is more potent than the combination of the parental antibodies, suggesting that cross-linking through both Fc receptors and PD-L1 results in enhanced CD27 agonist activity. In human CD27 transgenic mice, we observed that antigen-specific T cell responses to a vaccine in vivo are significantly more enhanced with a surrogate CD27/PD-L1 bsAb than with either individual antibody. Furthermore, the surrogate bsAb exhibits greater antitumor activity than the combination of the parental antibodies in a syngeneic lymphoma model. Taken together, these results suggest that the enhanced activity of CDX-527 can be attributed to more efficient cross-linking of the bispecific antibody acting on the CD27 receptor, resulting in stronger T cell activation, combined with efficient PD-1/PD-L1 blockade, providing a novel approach to immunotherapy of cancers. We have initiated development activities for CDX-527 including a pilot study in cynomolgus macaques to investigate the PK and PD properties and provide guidance for the design of a GLP toxicology study.

Citation Format: Laura A. Vitale, Lawrence J. Thomas, Thomas O'Neill, Jenifer Widger, Laura Mills-Chen, Andrea Crocker, Colleen Patterson, Anna Wasiuk, Eric Forsberg, James Boyer, Crystal Sisson, Jeffrey Weidlick, Shannon Renn-Bingham, Ioannis Papayannopoulos, Russ Hammond, Joel Goldstein, Henry C. Marsh, Tibor Keler, Li-Zhen He. CDX-527: A novel bispecific immune-modulating antibody targeting CD27 and PD-L1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2392.

Abstract 3816: Efficacy of CDX-1140, an agonist CD40 antibody, in preclinical tumor models

CD40 on antigen presenting cells plays a critical role in the induction of effective innate and adaptive immune responses. In contrast, CD40 signaling on certain malignant cells, particularly B cell lymphomas, inhibits proliferation or triggers apoptotic cell death. Thus, two independent mechanisms provide opportunities for the use of agonist anti-CD40 monoclonal antibodies in cancer therapy: enhancement of anti-tumor immunity, and direct inhibition of tumor growth. CDX-1140 is a human IgG2 antibody selected from a panel of fully human mAbs specific for CD40 generated by hybridoma technology from human Ig transgenic mice. We previously demonstrated the potent immune enhancing effects of CDX-1140 using in vitro models and in non-human primates. CDX-1140 was shown to activate dendritic cells and B cells in an Fc receptor independent manner. CDX-1140 does not bind to the CD40L binding site, and synergizes with CD40L in stimulation of the CD40 receptor and subsequent functional activities. Here we further characterized the anti-tumor activity of CDX-1140 on CD40 positive tumors using xenograft models in immunodeficient mice. Using the Ramos and Raji human lymphoblastoma cell lines, CDX-1140 was shown to attenuate tumor growth and prolong survival. Addition of CDX-1140 and human PBMC was highly effective at promoting complete rejection of both Ramos and Raji tumors. Importantly, the epithelial EJ138 bladder carcinoma cell line was also highly sensitive to CDX-1140 treatment. For example, in a study where mice received EJ138 cells subcutaneously, all animals that were treated with 300 µg of CDX-1140 on days 1, 8, and 15, showed suppression of tumor growth through day 60, in comparison to saline-treated animals which developed significant tumors in 7 of 8 animals. These data support the potential of CDX-1140 for direct anti-tumor effects on CD40-positive tumors (including epithelial tumors) that may supplement its activity as an immune activating agent. CDX-1140 is currently in a phase 1 dose-escalation study in patients with advanced solid tumors.

Citation Format: Lawrence J. Thomas, Li-Zhen He, James Testa, Anna Wasiuk, Jeffrey Weidlick, Crystal Sisson, Laura A. Vitale, Thomas O'Neill, Eric Forsberg, Catherine D. Pilsmaker, Lauren E. Gergel, Elizabeth Q. Do, James Boyer, April R. Baronas, Mallary Rocheleau, Michelle E. Grealish, Kathleen M. Borrelli, Henry C. Marsh, Tibor Keler. Efficacy of CDX-1140, an agonist CD40 antibody, in preclinical tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3816.

CD27-Mediated Regulatory T Cell Depletion and Effector T Cell Costimulation Both Contribute to Antitumor Efficacy

CD27, a member of the TNFR superfamily, is constitutively expressed in most T cells and plays crucial roles in T cell effector functions. The costimulation and antitumor activity of CD27 agonistic Abs have been well documented in mouse models. Clinical testing of a human IgG1 anti-CD27 Ab, varlilumab (clone 1F5), is ongoing in cancer patients. In this study, we set out to further understand CD27 as an immunomodulatory target and to address the mechanism of antitumor efficacy using different IgG isotypes of 1F5 in human CD27-transgenic mice. 1F5mIgG1, the only isotype engaging inhibitory FcγRIIB expressed in B cells, elicited the most potent and broad immune response, but terminal differentiation, exhaustion, and apoptosis in the activated effector T cells were inevitable. Accordingly, this isotype was the most effective in eradicating BCL1 lymphoma but had limited efficacy in s.c. tumors. Conversely, 1F5mIgG2a, which interacts with cells expressing activating FcγRs, led to moderate immune activation, as well as to prominent reduction in the number and suppressive activity of regulatory T cells. These combined mechanisms imparted potent antitumor activity to 1F5mIgG2a, particularly against the s.c. tumors. 1F5hIgG1, varlilumab, showed balanced agonistic activity that was prominent at lower doses and depleting activity that was greater at higher doses. 1F5hIgG1 had good antitumor activity in all tumor models tested. Thus, both agonist and depleting properties contribute to the antitumor efficacy of CD27-targeted immunotherapy, and modulation of these activities in patients may be achieved by varying the dose and regimen.

Abstract 3664: CDX-1402, a dendritic cell targeted fusion protein designed to elicit immunity to mesothelin and HER2 expressing tumors

The use of mAbs to target antigens to the endocytic receptor Dec205 on dendritic cells (DC) is an effective means to elicit helper and cytolytic T cell responses in the presence of appropriate adjuvants to activate DC. We have translated this concept to clinical studies using a fully human Dec205-specific mAb genetically altered to include the entire NY-ESO-1 cancer antigen (CDX-1401), which when combined with TLR agonists results in effective stimulation of both cellular and humoral NY-ESO-1-specific responses in cancer patients (Dhodapkar MV et al., Sci. Transl. Med. 6:232-251, 2014). Building on this concept, we developed a new fusion protein in which the Dec205 mAb is engineered to carry two tumor-related antigens in tandem [ECDs of mesothelin (MSLN) and HER2]. HER2 and MSLN are broadly expressed in selected tumor types and provide an expanded opportunity for this immunotherapy approach. We previously generated an anti-mouse DC-targeted HER2 vaccine (αDec205-HER2) and a MSLN vaccine (αDec205-MSLN) and demonstrated in mouse studies that they were potent in eliciting strong and broad CD4 T cell immunity, cross priming of CD8 T cells and humoral responses specific for HER2 or MSLN antigens, respectively. In this work we tested the impact of expressing two tumor antigens in the same construct on the immune responses to each antigen. Mice of various genetic backgrounds were immunized with equimolar amount of αDec205-HER2 (6.8 μg), αDec205-MSLN (5 μg) or αDec205-MSLN-HER2 (8.3 μg) in combination with poly IC-LC plus anti-CD40 or anti-CD27 as adjuvant. Similar levels of CD4 and CD8 T cell responses upon single or dual antigen vaccination were observed in the assessment of intracellular cytokines and IFNγ-ELISPOT after ex vivo stimulation with peptide pools derived from either HER2 or MSLN. High titers of anti-HER2 and anti-MSLN IgG, including IgG1 and IgG2a, were elicited upon αDec205-MSLN-HER2 vaccination. Both humoral and cellular responses were boosted by multiple dosing of the vaccine. Based on these data we developed CDX-1402 using our anti-human Dec205 mAb genetically fused to MSLN and HER2. CDX-1402 was shown to effectively deliver these antigens to human DC in vitro for activation of antigen-specific T cells. In vitro stimulation of healthy volunteer circulating T cells with autologous DC treated with CDX-1402 plus TLR agonist resulted in T cell cultures that produced IFNγ only when presented with CDX-1402-treated DCs or DC loaded with a select panel of HLA-I/II synthetic peptides derived from either MSLN or HER2 but not with control peptides. We also observed that T cells sensitized to CDX-1402 recognize cancer cell lines that express the vaccine antigen and HLA. Altogether, the data lend support for the use of CDX-1402 as a novel immunotherapeutic for treatment of multiple cancer types expressing MSLN and/or HER2.

Citation Format: Li-Zhen He, Jenifer Widger, James Testa, Laura Mills-Chen, Biwei Zhao, Jeff Weidlick, Crystal Sisson, Anna Wasiuk, Laura Vitale, Joel Goldstein, Henry Marsh, Tibor Keler, Venky Ramakrishna. CDX-1402, a dendritic cell targeted fusion protein designed to elicit immunity to mesothelin and HER2 expressing tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3664. doi:10.1158/1538-7445.AM2017-3664

Abstract 253: Synergistic antitumor activity of PD-1 signaling blockade and CD27 costimulation correlates with enhanced ratio of effector to regulatory T cells at the tumor site

Varlilumab (CDX-1127) is a fully human agonist antibody to CD27, a TNF receptor superfamily member expressed on the majority of T cells and subsets of NK cells and B cells. As such, varlilumab is an immunotherapy designed to harness the body's natural immune response by enhancing the activation of T cells that can specifically recognize and kill cancer cells. In an ongoing Phase 1 clinical trial, varlilumab has been very well tolerated and has demonstrated clear biologic activity and promising signs of clinical activity in advanced, treatment-refractory patient populations. This clinical data provides the rationale for combination studies with other immunomodulatory therapies, including inhibitors of PD-1 signaling. In this study we investigated the activity of varlilumab in combination with anti-PD-L1 using a disseminated murine B cell tumor, BCL1 in human CD27 transgenic mice. In this model of i.v. inoculated BCL1 cells, we have previously shown that varlilumab can delay tumor growth, but rarely results in cures. Despite expression of PD-L1, the BCL1 tumors were completely resistant to anti-PD-L1 monotherapy. However, the combination of varlilumab and anti-PD-L1 resulted in a significant improvement in survival and approximately 50% long-term survivors. To investigate the mechanism resulting in the synergistic activity, we collected spleens (the major site of tumor growth) from tumor bearing animals treated with individual or combined regimens and processed them for flow cytometry analysis. We found that animals treated with the combination of varlilumab and anti-PD-L1 had a higher ratio of infiltrating immune cells to tumor cells relative to monotherapy or saline controls. In particular, the ratio of effector (CD8+) T cells to Treg and the number of IFNγ+ CD4 and CD8 T cells were highly increased with the combination treatment. These data demonstrate that CD27 costimulation combined with checkpoint inhibition with anti-PD-L1 can result in improved immune profile in the tumor and synergistic survival benefit. This study, along with the good safety profile of varlilumab reported in the Phase 1 study, support the design of future combination studies in patients with cancer.

Citation Format: Lawrence J. Thomas, Li-Zhen He, Anna Wasiuk, Lauren E. Gergel, James M. Boyer, Sarah M. Round, Henry C. Marsh, Tibor Keler. Synergistic antitumor activity of PD-1 signaling blockade and CD27 costimulation correlates with enhanced ratio of effector to regulatory T cells at the tumor site. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 253. doi:10.1158/1538-7445.AM2015-253

Abstract 4949: Combined immunochemotherapy for poor prognosis breast cancer

Using preclinical mouse models of luminal B-type mammary adenocarcinoma (e.g., MMTV-PyMT mice), we, and others have reported that immune microenvironments of mammary tumors can be therapeutically manipulated to enhance responses to chemotherapy (CTX)(1). To determine the degree to which other subtypes of mammary carcinoma are similarly susceptible to immune reprogramming, we evaluated transgenic models of basal-like/triple negative (TN), e.g., C3(1)-Tag (2), and erbB2-amplified, e.g., Erbb2f/f/MMTV-Cre (3), mammary adenocarcinoma, with clinical/preclinical agents acting to either deplete or re-educate tumor-associated macrophages, in combination with taxol-based CTX, e.g., paclitaxel, nab-paclitaxel or eribulin mesylate. Our preliminary studies reveal similar complexity of immune cells infiltrating basal-like/TN tumors as what we previously reported for luminal B-type tumors where macrophages, as opposed to monocytes, are the predominate myeloid cells present. Significantly, mammary tumors in C3(1)-TAg mice exhibit improved responses to taxol-based CTX when given in combination with either colony stimulating factor-1 (CSF1) or CSF1 receptor (CSF1R) antagonists, as compared to either therapy alone, with no evident liver (ALT, AST, ALP) or kidney (Cre, BUN, CPK) toxicity. These studies reveal a synergistic benefit of combination macrophage-targeting immunotherapy with standard-of-care CTX regardless of mammary tumor subtype or form of taxol-based CTX. Thus, macrophage-targeting immunotherapy remains as an encouraging new neo-adjuvant strategy for slowing primary tumors and minimizing early metastasis. It remains to be determined if similar results will be realized with this class of agents in the metastatic setting.

1. DeNardo D, et al. Cancer Discov 1, 54-67 (2011)

2. Maroulakou I, et al., PNAS 91, 11236-11240 (1994)

3. Andrechek E, et al. PNAS 97, 3444-3449 (2000)

Support provided from the NCI/NIH (R01CA15531), the DoD (W81XWH-11-1-0702) and the Susan G Komen Foundation (KG110560, KG111084).

Citation Format: Anna Wasiuk, Hope Rugo, Lisa M. Coussens. Combined immunochemotherapy for poor prognosis breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4949. doi:10.1158/1538-7445.AM2013-4949

Mast cells impair the development of protective anti-tumor immunity

Mast cells have emerged as critical intermediaries in the regulation of peripheral tolerance. Their presence in many precancerous lesions and tumors is associated with a poor prognosis, suggesting mast cells may promote an immunosuppressive tumor microenvironment and impede the development of protective anti-tumor immunity. The studies presented herein investigate how mast cells influence tumor-specific T cell responses. Male MB49 tumor cells, expressing HY antigens, induce anti-tumor IFN-γ(+) T cell responses in female mice. However, normal female mice cannot control progressive MB49 tumor growth. In contrast, mast cell-deficient c-Kit(Wsh) (W(sh)) female mice controlled tumor growth and exhibited enhanced survival. The role of mast cells in curtailing the development of protective immunity was shown by increased mortality in mast cell-reconstituted W(sh) mice with tumors. Confirmation of enhanced immunity in female W(sh) mice was provided by (1) higher frequency of tumor-specific IFN-γ(+) CD8(+) T cells in tumor-draining lymph nodes compared with WT females and (2) significantly increased ratios of intratumoral CD4(+) and CD8(+) T effector cells relative to tumor cells in W(sh) mice compared to WT. These studies are the first to reveal that mast cells impair both regional adaptive immune responses and responses within the tumor microenvironment to diminish protective anti-tumor immunity.

Tryptophan hydroxylase-1 regulates immune tolerance and inflammation

Tryptophan hydroxylase deficiency in mast cells breaks allograft tolerance, induces tumor remission, and intensifies neuroinflammation.

Nutrient deprivation based on the loss of essential amino acids by catabolic enzymes in the microenvironment is a critical means to control inflammatory responses and immune tolerance. Here we report the novel finding that Tph-1 (tryptophan hydroxylase-1), a synthase which catalyses the conversion of tryptophan to serotonin and exhausts tryptophan, is a potent regulator of immunity. In models of skin allograft tolerance, tumor growth, and experimental autoimmune encephalomyelitis, Tph-1 deficiency breaks allograft tolerance, induces tumor remission, and intensifies neuroinflammation, respectively. All of these effects of Tph-1 deficiency are independent of its downstream product serotonin. Because mast cells (MCs) appear to be the major source of Tph-1 and restoration of Tph-1 in the MC compartment in vivo compensates for the defect, these experiments introduce a fundamentally new mechanism of MC-mediated immune suppression that broadly impacts multiple arms of immunity.

VISTA, a novel mouse Ig superfamily ligand that negatively regulates T cell responses

The immunoglobulin (Ig) superfamily consists of many critical immune regulators, including the B7 family ligands and receptors. In this study, we identify a novel and structurally distinct Ig superfamily inhibitory ligand, whose extracellular domain bears homology to the B7 family ligand PD-L1. This molecule is designated V-domain Ig suppressor of T cell activation (VISTA). VISTA is primarily expressed on hematopoietic cells, and VISTA expression is highly regulated on myeloid antigen-presenting cells (APCs) and T cells. A soluble VISTA-Ig fusion protein or VISTA expression on APCs inhibits T cell proliferation and cytokine production in vitro. A VISTA-specific monoclonal antibody interferes with VISTA-induced suppression of T cell responses by VISTA-expressing APCs in vitro. Furthermore, anti-VISTA treatment exacerbates the development of the T cell-mediated autoimmune disease experimental autoimmune encephalomyelitis in mice. Finally, VISTA overexpression on tumor cells interferes with protective antitumor immunity in vivo in mice. These findings show that VISTA, a novel immunoregulatory molecule, has functional activities that are nonredundant with other Ig superfamily members and may play a role in the development of autoimmunity and immune surveillance in cancer.

Mast cell degranulation breaks peripheral tolerance

Mast cells (MC) have been shown to mediate regulatory T-cell (T(reg))-dependent, peripheral allograft tolerance in both skin and cardiac transplants. Furthermore, T(reg) have been implicated in mitigating IgE-mediated MC degranulation, establishing a dynamic, reciprocal relationship between MC and T(reg) in controlling inflammation. In an allograft tolerance model, it is now shown that intragraft or systemic MC degranulation results in the transient loss of T(reg) suppressor activities with the acute, T-cell dependent rejection of established, tolerant allografts. Upon degranulation, MC mediators can be found in the skin, T(reg) rapidly leave the graft, MC accumulate in the regional lymph node and the T(reg) are impaired in the expression of suppressor molecules. Such a dramatic reversal of T(reg) function and tissue distribution by MC degranulation underscores how allergy may causes the transient breakdown of peripheral tolerance and episodes of acute T-cell inflammation.

Molecular mechanism and function of CD40/CD40L engagement in the immune system

SUMMARY

During the generation of a successful adaptive immune response, multiple molecular signals are required. A primary signal is the binding of cognate antigen to an antigen receptor expressed by T and B lymphocytes. Multiple secondary signals involve the engagement of costimulatory molecules expressed by T and B lymphocytes with their respective ligands. Because of its essential role in immunity, one of the best characterized of the costimulatory molecules is the receptor CD40. This receptor, a member of the tumor necrosis factor receptor family, is expressed by B cells, professional antigen-presenting cells, as well as non-immune cells and tumors. CD40 binds its ligand CD40L, which is transiently expressed on T cells and other non-immune cells under inflammatory conditions. A wide spectrum of molecular and cellular processes is regulated by CD40 engagement including the initiation and progression of cellular and humoral adaptive immunity. In this review, we describe the downstream signaling pathways initiated by CD40 and overview how CD40 engagement or antagonism modulates humoral and cellular immunity. Lastly, we discuss the role of CD40 as a target in harnessing anti-tumor immunity. This review underscores the essential role CD40 plays in adaptive immunity.

Mast cells as regulators of adaptive immunity to tumours

The observation that mast cells accumulate at the periphery of growing tumours is now well documented, and the loss of mast cells correlates with reduced tumour growth. The role of mast cells as innate regulators of both inflammatory and immunosuppressive responses slowly becomes clear as novel tools become available. This review will address the role of mast cells in tumours and how they can interact with the local immune environment to mediate immune suppression contributing to tumour escape.

Dendritic cells require the NF-kappaB2 pathway for cross-presentation of soluble antigens

NF-kappaB-inducing kinase (NIK) is responsible for activation of the non-canonical p100 processing pathway of NF-kappaB activation. This kinase has been shown to be critical for activation of this pathway after signaling through several TNF family members including CD40. The functional importance of this pathway in CD40 and TLR-induced dendritic cell (DC) differentiation was studied in vivo in the alymphoplasia (Aly) mouse. The Aly mouse expresses a mutant NIK molecule that prohibits the induction of the non-canonical pathway. We show that while MHC class II presentation and in vivo migration of Aly DCs is intact, these cells are unable to cross-prime CD8+ T cells to exogenous Ag. Gene expression array analysis of DCs matured in vivo indicates multiple defects in Ag processing pathways after maturation and provide a global view of the genes that are regulated by the NF-kappaB2 pathway in DCs. These experiments indicate a possible role for NIK in mediating cross-priming of soluble Ag. In addition, our findings explain the profound immune unresponsiveness of the Aly mouse.